Study On Phytoplankton Community In The Bay Of Bengal And The Equatorial Region Of Eastern Indian Ocean

In this study,a comprehensive survey of phytoplankton community structure in the Bay of Bengal in the autumn of 2016 and the equatorial region of eastern India Ocean and its adjacent sea area in the spring of 2017 were investigated.The equatorial region of eastern Indian Ocean phytoplankton survey took two different sampling methods,namely concentrated water sample and vertical trawl method.Through comparing cell abundance and species diversity of the two kinds of sampling nethods,The study compared the differences between the two kinds of sampling methods,providing a scientific basis for the comprehensive investigation of phytoplankton community.Based on the preliminary analysis of phytoplankton community in the Bay of Bengal,the equatorial region of eastern India Ocean.It aim to provide basic research data for future related waters and lay the foundation for,further research and investigation.A total of 408 taxa(including variety form and unidentified taxa)of phytoplankton that belong to 85 genera of 5 phyla were identified,in which 25 genera and 236 species were Pyrrophyta,while 53 genera and 160 species were Bacillariophyta,3 genera and 8 species were Chrysophyta,and 3 genera and 4 species were Cyanophyta.These species were warm oceanic and tropic oceanic species primarily,which indicated that the climate of the was tropical and subtropical.The abundances of phytoplankton was different in the survey sea area and the survey season.In 2016,the average abundance of phytoplankton cells in the Bay of Bengal was 3.86× 105 cells/m3,While the mean cell abundance of net phytoplankton in the equatorial region of Eastern India Ocean was 4.07×105 cells/m3 in the spring of 2017 years,while the average cell abundance of the concentrated samples was 4.99×105 cells/m3.The abundance of phytoplankton cells wascontributed by diatom and Cyanobacteria.The distribution of phytoplankton was determined by the distribution of diatom,because diatom has good adaptability to the sea environment.In 2016,the high value of phytoplankton was located at the station IFB03 in the 10°-15° N region,and the maximum of 2017 cell abundances appeared at the equatorial region.The dominant species of the Bay of Ben gal were Thalassiothrix longissima,Thalassionema frauenfeldii,Leptocylindrus mediterraneus,Cyclotella striata var.striata,Fragilariopsis doliolus,Ceartium furca,Pseudo-nitzschia delicatissima,Thalassionema nitzschioides,Dictyocha fibula and so on;The dominant species of Estern Indian Ocean were Cyclotella striata var.striata,Pseudo-nitzschia pungens,Thalassiothrix Longissima,Thalassionema frauenfeldii,Synedra spp.,Thalassionema nitzschioides,Leptocylindrus mediterraneus,Nitzschia spp.,Fragilariop.sis doliolus,Lanktoniella foromsa,Thalassiosira excentrica and so on.From 2016 to 2017,the S-W diversity index was 3.11 and 2.87 respectively,and Pielou evenness index was 0.472 and 0.407 respectively.The cell abundances of Ruchelia intracellularis was relatively low,there is unnoticeable change in shape.The abundance of T.thiebaultii in the Bay of Bengal was higher than that in the equatorial region of eastern Indian Ocean.And the distribution trend of T.thiebaultii were very similar.and it was the most important species.The structure of phytoplankton community in the Bay of Bengal and the equatorial region of eastern India Ocean wassimilar.The distribution of phytoplankton was greatly affected by ocean cuurents and water masses.Inter annual variation of dominant species with Cyanobacteria was relatively large.Diatom related relationships were more complex.The correlation of Chrysophytais better.Most dominant species in the Bay of Bengal had positively correlation with Cyanobacteria,while the equatorial region of Eastern India Ocean had negatively correlation with Cyanobacteria abundances.Most dominant species in the Bay of Bengal were positively correlated with ammonium nitrite and silicate,Due to the thermocline,while the nitrate concentration in the equatorial region of Eastern India Ocean in 2017 was extremely high,and most dominant species were positively correlated with ammonium.and no significant relationship with other nutrient.